Fuel Processor, Components Thereof and Operating Methods Therefor

Abstract

Fuel processors include at least one of a fuel introduction tube, a critical flow venturi and / or a heat exchanger along with other components. Such fuel processors are particularly suitable for use in engine system applications where a liquid fuel is introduced into an oxidant stream comprising hot engine exhaust gas, for downstream conversion in the fuel processor to produce a hydrogen-containing gas stream, such as a syngas stream.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)[0001]This application is related to and claims priority benefits from U.S. Provisional Patent Application Ser. No. 60 / 864,319 filed Nov. 3, 2006, entitled “System And Method For Introducing A Fuel Stream Into An Engine Exhaust Stream”; Ser. No. 60 / 864,240 filed Nov. 3, 2006, entitled “Syngas Generator With Metering, Mixing And Flashback Arresting Device”; Ser. No. 60 / 864,248 filed Nov. 3, 2006, entitled “System And Method For Mixing A Fuel Stream And An Engine Exhaust Stream In A Fuel Processor”; Ser. No. 60 / 915,116 filed May 1, 2007, entitled “Syngas Generator”; and Ser. No. 60 / 954,803 filed Aug. 8, 2007, entitled “Syngas Generator”, each of which is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates to fuel processors for producing a hydrogen-containing gas stream. The improved fuel processor includes at least one of a fuel introduction tube, a critical flow venturi or a heat exchange...

AI Technical Summary

Benefits of technology

[0021]A fuel introduction tube can be used to introduce a liquid fuel stream (herein meaning a fuel that is a liquid when under IUPAC defined conditions of standard temperature and pressure) into an oxygen-containing gas stream which is at a temperature above the boiling point of the liquid fuel, for downstream chemical conversion in a fuel processor. In preferred embodiments, the fuel introduction tube is thermally shielded from the hot oxygen-containing gas stream to reduce boiling of the fuel which would otherwise occur within the fuel introduction tube, and preferably to maintain the liquid fuel stream below its boiling point within the introduction tube.

[0034]The supply of a reactant stream to the fuel processor can be passively metered by directing it through the venturi. Thus, the need for active flow control devices associated with the fuel processor can be reduced or eliminated at least for one of the reactants.

[0052](iii) at least one ignition source that in some embodiments is located within the reaction chamber. Shielding can be employed to decrease the speed of the reactant streams around the ignition source or to protect them from radiant heat from the reaction process. Examples of suitable ignition sources include one or more of a glow plug, a spark igniter, or an electrical resistance wire.

[0063]In preferred embodiments, during step (b) the oxidant stream flows through the heat exchanger in an essentially co-flow direction in relation to the product stream, although it can flow in a counter-flow or other configuration. The product stream, as it flows in contact with the heat exchanger, can contain some unreacted fuel and / or oxidant. Preferably the venturi is operated at a choked condition for a predominant portion of the time during normal operation of the fuel processor. The combined reactant stream can be directed to the reaction chamber via a mixing tube. The mixing tube can house the sonic shock wave when the venturi is choked, and can be used to prolong the mixing duration (and vaporization duration if applicable) of the fuel and oxidant streams upstream of the reaction chamber.

[0065]The combined reactant stream can be directed past a bluff body into the reaction chamber where it is converted to the product stream. The bluff body can modify the flow characteristics of the combined reactant stream as it enters the reaction chamber. For example, it can increase the speed of the combined reactant stream upstream of the reaction chamber or near the exit of the mixing tube to prevent flashback, and / or can help redistribute the combined reactant stream as it enters the reaction chamber and create a reflux zone downstream of it to stabilize the flame.

Problems solved by technology

Flashback is uncontrolled combustion that can occur and propagate back from the combustion zone into to the mixing zone in the fuel processor.

However, such “active” reactant metering systems, with multiple moving and interconnected components, typically add to the overall complexity and cost of the system; reduce system reliability and durability; increase the likelihood of fluid leakage; and slow the dynamic response time of the fuel processor.

Conversion of liquid fuels, especially heavy hydrocarbons, can be difficult due to the various components that make up the fuel that react at different temperatures and rates.

Inadequate vaporization and mixing of the fuel with the oxidant stream can lead to localized fuel-rich conditions, resulting in the formation of coke or soot (carbon), and can also adversely affect the fuel conversion efficiency.

Chemical decomposition of the fuel can also lead to carbon formation starting at temperatures as low as about 200° C. Carbon deposits can impede the flow of gases in the fuel processor and downstream devices, increasing the back pressure in the system.

The temperature of the engine exhaust stream can reach over 600° C., but at such elevated temperatures there is a limited time in which to effectively vaporize and mix the two streams before undesirable carbon forming reactions will start to occur.

Furthermore the wide spray pattern can cause fuel to be sprayed onto the interior walls of the fuel processor creating a “wall wetting” effect that can create undesirable localized fuel-rich conditions.

Prior devices that have been used to introduce a liquid fuel into hot oxidant streams, such as hydraulic nozzles, air-assist nozzles and injectors, suffer from additional shortcomings.

There is typically a high pressure drop across such devices, thus significant fuel supply pressure and energy is required.

They can be fouled and / or plugged up by various solids and deposits, resulting in increasing pressure drop over time.

Also they typically have a limited turndown ratio, plus they can be expensive, heavy and / or bulky.

Under high temperature conditions internal fuel boiling within the device can interrupt the flow of fuel through it.

Furthermore, the higher mass flow rates typical of prior devices are not necessarily suitable for applications requiring relatively low volume hydrogen production.

The use of valves or heat absorbing devices can add to the pressure drop across the fuel processor, as well as to the system cost, weight and complexity.

There are some particular challenges associated with the design of fuel processors used in engine systems to convert a fuel and oxidant stream comprising engine exhaust into a hydrogen-containing stream.

Metering the engine exhaust stream supplied to the fuel processor is therefore a challenge due to the significantly variable exhaust gas supply.(b) The engine exhaust stream pressure is limited, especially at idle conditions, so the pressure available to aid in the mixing and distribution of fuel in the engine exhaust stream is sometimes limited.(c) High engine exhaust back-pressure can decrease engine efficiency and performance, increasing the operating cost.

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